Warren E. Thompson

The vibrational spectra of molecular ions isolated in solid neon. IX. HCN+, HNC+, and CN−

When a Ne:HCN sample is codeposited at ∼5 K with a beam of neon atoms that have been excited in a microwave discharge, infrared absorptions of HNC, HCN+, and CN− appear. The absorptions of HNC isolated in solid neon are considerably closer to the gas‐phase band centers than are the previously reported argon‐matrix absorptions. The CH‐stretching fundamental of HCN+ is identified, and the two stretching force constants of HCN+ are determined, using the isotopic data obtained in this study and the CN‐stretching frequencies of HCN+ and DCN+ obtained in earlier photoelectron spectroscopic studies. In the inert, nonpolar environment provided by the neon matrix, the infrared absorption of CN− appears at 2053.1 cm−1, very close to the position obtained in two recent ab initio calculations. HCN+ photoisomerizes to HNC+ with a threshold in the near‐infrared spectral region, consistent with an earlier ab initio calculation of the position of the transition state for this process. The reverse photoisomerization has a...

The vibrational spectra of molecular ions isolated in solid neon. XI. NO+2, NO−2, and NO−3

When a Ne:NO2 or a Ne:NO:O2 sample is codeposited at approximately 5 K with a beam of neon atoms that have been excited in a microwave discharge, infrared absorptions of NO+2, NO−2, and NO−3 appear. Detailed isotopic substitution studies support the assignment of prominent absorptions to ν3 of NO+2 and NO−2 and of weak to moderately intense absorptions to the ν1+ν3 combination band of each of these species. When the contribution of anharmonicity is considered, the positions of the NO+2 absorptions are in satisfactory agreement with the values for the stretching fundamentals obtained in a recent gas‐phase study of that species. When the sample is exposed to 240–420 nm mercury‐arc radiation, the initially present absorptions of NO−3 trapped in sites with a small residual cation interaction diminish in intensity, and the unsplit ν3(e’) absorption of isolated NO−3 grows. The mechanism responsible for this growth in the absorption of isolated NO−3 is considered.

Infrared Spectra of trans-HOCO, HCOOH+, and HCO2- Trapped in Solid Neon

When a Ne:HCOOH sample is codeposited at ca. 5 K with neon atoms that have been passed through a microwave discharge, new absorptions appear in the infrared spectrum of the resulting solid that can be assigned to trans-HOCO, trans-HCOOH+, and HCO2−. The absorptions of trans-HOCO are readily identified by a comparison with those previously reported for that molecule trapped in solid argon. Preliminary assignments of infrared absorptions of HOCO+, confirmed in studies using another experimental system, are also suggested. The identifications of trans-HCOOH+ and of HCO2− are aided by study of the photodestruction characteristics of these products when the deposit is exposed to various wavelengths of visible and ultraviolet radiation, by an analysis of the spectra obtained from isotopically substituted samples, and by a comparison with the results of ab initio and density functional calculations. Three previously unidentified vibrational fundamentals of trans-HCOOH+ have been assigned, as have been four vibra...

Evidence for the stabilization of rectangular O+4 in solid neon

The reassignment of the 1320 and 2949 cm−1 absorptions of O+4, previously attributed to the trans isomer, is considered. A satisfactory least‐squares force constant fit of the isotopic data for these two absorptions, assuming a rectangular structure, has been obtained. In accord with the results of ab initio calculations by Lindh and Barnes, it is concluded that, as previously proposed, the 1164 and 2808 cm−1 absorptions should be assigned to the trans ground state of O4+O, but that the rectangular isomer, which they calculated to lie at only slightly higher energy, may contribute the 1320 and 2949 cm−1 absorptions.

The vibrational spectra of molecular ions isolated in solid neon. X. H2O+, HDO+, and D2O+

When a Ne:H2O≥200 sample is codeposited at approximately 5 K with a beam of neon atoms that have been excited in a microwave discharge, new infrared absorptions appear close to the gas‐phase band centers of the three vibrational fundamentals of H2O+. Detailed isotopic substitution studies confirm this assignment and provide assignments for all of the vibrational fundamentals of HDO+ and D2O+. When ions are present in the neon matrix, rotation of a significant fraction of the water molecules is inhibited. Electrons produced by the photodetachment of anions, which must be present to maintain overall charge neutrality of the deposit, accelerate nuclear spin equilibration of water in the matrix. As the concentration of H2O+ is decreased by capture of the photodetached electrons, the absorptions assigned to nonrotating water are also reduced in intensity. The nature of the other ionic species which may be present in the sample is considered.

The infrared spectroscopy and photochemistry of NO3 trapped in solid neon

NO(3) can be stabilized in solid neon either by codeposition at 4.3 K of a Ne:O(2) mixture with a Ne:NO mixture that has been passed through a microwave discharge or, in higher yield, by codeposition of a Ne:NO mixture with a Ne:O(2) mixture, followed by annealing of the deposit at approximately 7 K and exposure of the solid to near ultraviolet radiation. All of the previously reported bands of NO(3) between 700 and 3000 cm(-1) were observed, most with neon-matrix shifts of less than 2.5 cm(-1). The infrared spectra of eight isotopic species of NO(3) were obtained. The observed isotopic shifts demonstrate the occurrence of extensive mixing of ground-state levels of e() symmetry and their strong vibronic interaction with the B (2)E() state. Photodissociation of NO(3) by irradiation of the deposit at wavelengths longer than 520 nm leads to new absorptions near the fundamentals of NO and O(2) and other new absorptions at relatively low frequencies. These absorptions were depleted and NO(3) regenerated by subsequent near ultraviolet irradiation of the deposit, suggesting the stabilization of a weakly bound NO(O(2)) complex in solid neon.

The vibrational spectra of molecular ions isolated in solid neon. XVI. SO2+, SO2−, and (SO2)2−

When a Ne:SO2 mixture is subjected to Penning ionization and/or photoionization by neon atoms in their first excited states, between 16.6 and 16.85 eV, and the products are rapidly frozen at approximately 5 K, the infrared spectrum of the resulting deposit includes absorptions assigned with the aid of isotopic substitution studies to SO, SO2+, SO2−, (SO2)2−, and, tentatively, SO−. The fundamental and first overtone absorptions of SO lie 0.9 and 1.8 cm−1, respectively, below the gas-phase band centers. Ab initio calculations at the Hartree–Fock level show an instability in the v3 vibration of SO2+ which is avoided by higher-level calculations. The ν3 and ν1 fundamentals of SO2− isolated in solid neon are identified at 1086.2 and 990.8 cm−1, respectively. In agreement with an earlier proposal, the 1042 cm−1 absorption originally assigned to ν3 of SO2− trapped in solid argon is reassigned to MSO2, with M an alkali metal. Near the photodetachment threshold for SO2− isolated in a neon matrix, electron capture ...

The Reaction of BF3 with H2O. Infrared Spectrum of BF2OH Trapped in Solid Neon

When a Ne:BF3 sample is passed through a long stainless steel deposition line before being frozen onto a cryogenic observation surface maintained at approximately 5 K, the infrared spectrum of the resulting deposit includes prominent absorptions assigned to BF2OH and weaker absorptions contributed by F311B–OH2. Pretreatment of the deposition line with isotopically substituted water leads to the appearance of absorptions of the 18O- and D-substituted products. The assignments are supported by the results of ab initio calculations at several different levels and by a least-squares force constant fit to the infrared absorptions of the isotopomers of BF2OH. The thermochemistry of the reactions of BF3 and H2O to form F3B–OH2 and to form BF2OH+HF has been calculated at the G2 level. Although the heats of reaction calculated for 298 K somewhat favor formation of the complex, when the entropy is also considered the two reactions become more competitive.

Infrared spectra of (NO)2+, (NO)2−, and (NO)3− trapped in solid neon

New studies of the infrared spectra of the products which result on codeposition at approximately 5 K of a Ne:NO sample with Ne atoms that have been excited in a microwave discharge have led to new and revised assignments for several ionic species. The appearance of the ν1 absorption of ONNO+ for several new species with asymmetric isotopic substitution, but for no symmetrically substituted species, confirms the trans ground-state configuration for ONNO+. The behavior of a neon-matrix product absorption at 1227.5 cm−1 parallels that of an argon-matrix absorption at 1221.0 cm−1 which has recently been assigned to trans-ONNO−. The identity of the carrier of a product absorption at 1424.1 cm−1, contributed by a vibration of two symmetrically equivalent NO groups, has not been definitively established. This absorption exhibits complex photodestruction behavior. Three absorptions are assigned to cis,cis-(NO)3−, which has C2v symmetry, with the aid of density functional calculations of the isotopic substitution pattern for the vibrational fundamentals of this species. Similar calculations of the isotopic substitution patterns for other structures result in poor agreement with the experiments. Photodestruction of cis,cis-(NO)3− trapped in solid neon yields the N2O⋯NO2− complex.

The vibrational spectra of molecular ions isolated in solid neon: HCCH+ and HCC−☆

Abstract When a Ne:C 2 H 2 sample is codeposited at approximately 5 K with a beam of neon atoms that has been excited in a microwave discharge, a sharp, prominent absorption assigned to ν 3 of HCCH + appears at 3137.6 cm −1 , very close to the previously reported gas-phase band center. Experiments on carbon-13 and deuterium substituted samples support this assignment and permit the identification of all of the infrared-active CH- and CD-stretching fundamentals of the isotopically substituted acetylene cations, as well as the determination of the stretching and stretching-interaction force constants. The absorptions of the carbon-13 substituted acetylene cations have also been identified in the analogous argon-matrix experiments, but exhibit a matrix shift of approximately 30 cm −1 , possibly because of the larger polarizability of argon. The ν 3 absorption of H 13 C 13 CH + isolated in a neon matrix is split by interaction with a combination band, probably ν 2 + ν 4 + ν 5 (Σ u + ). The CC-stretching fundamental of HCC − has been tentatively identified at 1773.0 cm −1 , and the band origin of the A 2 Π u - X 2 Σ g + transition of C 2 − near 4155 cm −1 , in neon-matrix experiments.